Copy registration patch into installation directory and apply.
Register with any name and registration code number.
Done. Now you have Paid Mode.
Eudora.6.x.reg/keygen/CORE.TXT
1. Install eudora, run it once to make sure eudora.ini is created.
2. Try to locate eudora.ini with your explorer (usually in Documents and Settings//Application Data/Qualcomm/Eudora)
3. Put the keygen in the same directory of eudora.ini
4. Run eudora, go to 'payment/registration', click above 'paid mode'
Done :)